Telephone circuit



C. (3. CASH TELEPHONE CIRCUIT Filed Dec. 17, 1931 Dec. 13, 1932.

w rLLLL E F m Banal Pass INVENTOR 6.6.M9/4y BY NTTORNEY patented Dec.13, 1932 UNITED mm PATENT OFFECE' CLAUDE 0. CASE, OF YORK, N. Y.,ASSIGNOR TO AMERICAN TELEPHONE AND TELEGRAPH COMPAE'Y, A CORPORATION OFNE'W YORK TELEPHONE CIRCUIT Application filed December 17, 1931. SerialNo. 581,753.

This invention relates to telephone systems, and more particularly tomeans for preparing the linesof such systems, whch may have protectiveor remedial devices connected thereto, for the application of directcurrent for testing purposes. ,7 A telephone circuit under certainconditions might have various remedial or protective devices connectedthereto such, for example, as dra nage coils or transformers. Theconnection of drainage coils to the telephone line might be desirable toshunt to ground induced currents of relatively low frequency, such as inthe neighborhood of 60 cycles, and transformers might be utilized toisolate sections of the line for various purposes. A telephone line ofthis type is not adapted forthe application of direct current theretofor testing purposes because of the remedial or protective devicesassociated therewith. Accordingly it is one of the primary objects ofthis invention to provide arrangements for so connectng such remedial orprotective devices to a line that they can readily be disconnectedtherefrom, when it is desired to conduct testing operations thereon withdirect current. Other objects and features of the invention will appearmore fully from the detailed description thereof here nafter given.

The invention may be more fully understood from the followingdescription, together with the accompanying drawing in the Figures 1, 2and 3 of which the invention is illustrated. Figure 1 is a circuitdagram showing how a protective device, such as a drainage coil, mightbe disconnected from a line when desired. Fig. 2 is a modification ofFig. 1. In Fig. 3 is shown a means for including in or exclud ng from aline a remedial device, such as a transformer. Similar referencecharacters have been utilized to denote like parts in all of thefigures.

In Fig. 1 are shown a group of transmission lines L L and L These linesmight have remed al or protective devices connected thereto such as thedrainage coils 1, 5 and 10. The drainage coils 5 and 10 are connected tolines L and L over the contacts of relays 4 and 9, respectively. Theline L may be used as a control circuit. If it should be desired toapply direct current to lines L or L for the purpose of conducting teststhereon, a control current would be sent over a metallic circuitcomprising the l ne L. This current might have a frequency. of the orderof 135 cycles. This current would not be shunted to ground by thedrainage coil 1 as this coil is designed to shunt to ground longitudinalcurrents of relativelylow frequencies, such for example, as 60-cycles-Thecontrol cur.- rent would be transmitted over circuit'2 and throughthe band-pass filter 3 and would operate the relay i. Th s woulddisconnect the drainage coil 5 from the line L and prepare it for theapplication of direct current for testing purposes. The operation ofrelay 1 would also close the following circuit: from battery 7, armatureand contact 6 of relay 4, conductor 8, winding of relay 9 to ground.This would operate relay 9 and disconnect the drainage coil 10 from lineL and thus prepare lne L for the application thereto of direct currentfor testing purposes. Other contacts might be provided for the relay 5to disconnect other drainage coils from other lines if desired. Theband-pass filter 3 will prevent the arrangements from functioning oncurrents other than the con trol frequency. It is desirable to have thecontrol circuit L over which the 135-cycle control currents aretransmitted, equipped with apparatus such as drainage coil 1. If thedrainage coil 1 were omitted from line L, it is possible that (SO-cycleinduced currents might break down the protector blocks at the centraloflice and this would result in the transmission of oscillatory currentsover the line L. Those osc llatory currents might have frequencieswithin the range of the band-pass filter 3 and hence cause falseoperation of the equipment. The provision of the drainage coil 1 .in thecontrol circuit will prevent the breaking down of the protector blocksand the false operation of the apparatus attendant thereon. The bandpassfilter 3 obviously prevents the false operation of the apparatuson voicecurrents or the 60-cycle induced currents.

In Fig. 2 is shown a modification of the arrangements of Fig. 1. Similarreference characters have been utilized to denote like parts in bothfigures. In Fig. 2 a direct current relay 14 is substituted for thealternating current relay 4 of Fig. 1. A rectifier 15, which might be ofthe copper oxide variety, is connected between relay 14 and the bandpassfilter 3. The drainage coil 5 is connected to line L over .the contactsof relay 14. As the operation is substantially similar to that of Fig.1, no further description thereof will be given. v

In Fig. 3 is shown a telephone line L; in which is included atransformer 25. Obviously it would be desirable to d sconnect thetransformer from'the line if direct current were to be applied theretofor testing purposes. Accordingly, a circut 18 is bridged across theline between the central ofiice and the transformer. This circuit wouldinclude a bandpass filter 21 transmitting a band of frequencies in theneighborhood of 135 cycles. The circuit 18 would also include arelay'22. The windings of transformer 25 are connected to line L v overthe break contacts of this relay. vV hen 135-cycle current istransmitted over the line, the relay will operate and the line L will becompleted directly over the make contacts of relay 22 and thetransformer windings will be excluded from the line. In order that thedirectcurr'ents applied to the line L, for testing purposes may notaffect circuit 18, the condensers 19 and 20 are included therein.Further c rcuits, such as 18, with'relays,

such as 22, mightbe included in the line.

Under such conditions the application of control current tothe linewould disconnect other transformers, or translating devices such asdrainage coils, from the-line.

VVhile the invention has been d sclosed as embodied in certain specificforms which are deemed desirable, it is understood-that it is capableof'embodiment in many and other widely varied forms without departingfrom the'spirit of the invention as defined by the appended claims.

That is claimed is:

1. A telephone system comprising a line in which a translating deviceis'connected,

a circuit bridged across said line selective for a certain band offrequencies, relay meansin said selective circuit, a second telephoneline, and a translating device connectedin said second telephone overthe con- =tacts of said relay.

2. Atelephone system comprising a line, a drainage 0011 connected acrosssaid line and designed to shunt out currents of relatively lowfrequencies, a circuit bridged across said line, a band pass filterinsaid circuit designed to pass aband of frequencies above therelatively low frequencies shunted by said drainage coil, a relayconnected'to "saidcircuit, a second'telephone'line, and a drainage coilconnected across said second telephone line over the contacts of saidrelay.

3. A telephone system comprising a line across which a protective deviceis connected, a circuit bridged across said line selective for a certainband of frequencies, relay means in said selective circuit, a secondtelephone line, a protective device connected across said secondtelephone line over the contacts of said relay, a second relaycontrolled by said first relay, a third telephone line, and'a protectivedevice connected across said third telephone line over the contacts ofsaid second relay;

1. A telephone system comprising a line across which a protective deviceis connected, a circuit connected across said line selective for acertain band of frequencies, rectifying means in said selective circuit,relay means controlled by the output of said rectifying means, a secondtelephone line, and

a protective device connected across said second telephone line over thecontacts of said relay means.

5. A telephone system comprising a line, a circuit selective for acertain band of frequencies connected acrosssaid line, a relay in saidselective circuit, a transformer having its windings connected incircuit in said line whensaid relay is not operated and disconnectedtherefrom when said relay is operated, and means operative when saidrelay is operated for directly connecting together the sections of saidline previously connected to said transformer windings.

In testimony whereof, I have signed my name to this specification this15th day of December, 1931.

CLAUDE 0. CASH.

